The present invention relates generally to derrick hoisting equipment and particularly to slip type derrick elevators which grip and support pipe, tubing, and casing when running into or out of the well bore.
During drilling operations, it is necessary to periodically remove the string of drill pipe from the well bore. The drill string is separated into sections or stands of pipe from 60 to 90 feet in length and the stands are racked in an upright position in the derrick. The typical elevator has two body sections which are pivotally attached to open and close about the pipe. Ears are provided on the elevator to support the same by means of links which are attached to the hook and traveling block. When the two body sections of the elevator are latched into position about the pipe, the top surface of the elevator forms a shoulder upon which the pipe external upset rests. By raising the elevator, the stand of pipe can be maneuvered into position on the derrick.
Slip type elevators are customarily used with casing and tubing which have less pronounced upsets than drill pipe. The slips of a slip type elevator support the tubing or casing by a wedging action of the slips between the tubing or casing and the tapered surface of the elevator bowl. The slips are forced into contact with the tubing or casing by contact of the external upset onto the top of a disk-shaped plate commonly referred to as the slip setting ring. The slip setting ring, in turn, contacts the top of the slips and forces them down in the tapered bowl of the elevator. As the slips move downward in the bowl, the tapered surface causes the slips to move radially inward to contact the tubing or casing. Slip-type elevators utilizing slip setting rings are shown, for instance, on page 26 of the BJ-HUGHES Inc. 1978-79, Composite Catalogue, entitled "Oilfield Products and Systems."
A recurring problem in the use of slip-type derrick elevators is the binding of the slip setting ring on the taper of the upset of the pipe, tubing, or casing during setting of the slips. This problem is especially distressing when coming out of the well bore since the derrick man must attempt to "unstick" the slip setting ring. Attempts have been made to provide slip-type elevators with modified bowl configurations in order to alleviate the problem. However, when worn, these slip setting rings also stick. Other designs have embodied a molded rubber insert bonded to the inner surface of the setting ring but have similarily been unsuccessful in preventing sticking.